Hydraulic jars are described in the prior art. For example, Gore Kemp, in Oilwell Fishing Operations: Tools and Techniques. Gulf Publishing Company/Book Division/Houston, London, Paris, Tokyo), discloses a jar, which contains a cylinder connectable to a stuck object and filled with fluid. The cylinder encloses a piston, which is connected via a rod to a work string of pipes (a pipe string), wherein the rod inlet in the cylinder is sealed with a packer. To make a stroke by using the tension of the pipe string, the piston is loaded to create pressure on the working fluid in the cylinder above the piston. Due to leakage of working fluid through the pair “cylinder-piston”, the piston moves upwards and reaches in the cylinder an area with expanded bored diameter. As a result, the pressure in the said area of piston rapidly drops that causes the stretched (deformed) pipe string to contract quickly under elastic forces, whereupon the piston strokes the top part of the cylinder.
The disadvantage of the above described jar is low efficiency, due to the fact that the pair “piston-cylinder” is made with a significant gap, otherwise return of the piston back to original position becomes difficult. As a result, the above described jars can operate only under relatively low pressure drops on piston during upstroke that limits deformation of pipe string and, hence, impact force.
A hydraulic jar [RU patent 2272122 C2, Int.Cl. E21B 31/113, publ. Mar. 20, 2006], which includes a cylinder, a piston connected to a tractive rod and a compensative rod, which are sealed with packers arranged at butt ends of cylinder, can be chosen as the closest prior art. Cylinder cavities separated by the piston are in a fluid connection by means of a channel, which is provided with a back valve. The channel connecting the cylinder cavities is made in the form of annulus between the compensative rod and the piston. A bush with external bevel positioned above the piston on the compensative rod, together with the piston butt end forms a groove. A groove is provided with a conduit running along the groove bottom, the conduit being in a fluid connection with the annulus formed between the piston and the compensative rod. An elastomer <<O>> ring is placed in the groove for preventing fluid from flowing in the opposite direction.
The disadvantage of this design is that when using a jar with BHA in drilling process there is a possibility of unauthorized (accidental) jar operation as result of normal axial operational loads, for example when a bit is being lifted off the bottom or in the course of tripping process. This situation is frequently observed in practice and often causes failure of BHA telescopic system electronic components due to impacts, and further may result in overloads of the pipe string with undesired dynamic forces.
One approach to solve the above described problem is providing a jar having a fixed bush. For example, in a jar described in patent RU 2230880, publ. Jan. 20, 2004 movable jar parts are fixed by means of a destructive bush. However, the above described technical solution provides connection of movable jar parts only once, before it is used for the first time. Later, after the dislodging, the jar needs to be pulled out to replace a destructive plug. Otherwise, in subsequent drilling operations after the dislodging operation the jar can be subjected to unauthorized accidental impacts that reduce the jar life time and may cause inconveniences when handling drill pipes.
Another drawback of the above described prior art jar constructions is that they do not allow to induce torque impacts in addition to axial impacts that significantly limits the possibilities of retrieving a stuck equipment.
RU 2291275, C2, E21B31/113, publ. Aug. 20, 2007, discloses a jar construction, wherein a splined connection of the body and spindle is made in the form of a helical curve that enables the jar to make both torsion and axial impacts. However, this technical solution does not prevent accidental unauthorized actuation of the jar mechanism in cases when rotation torques can occur in addition to axial loads, for example in rotary drilling, and overloads the pipe string with undesired dynamic forces.
Thus, there is an existing need to provide a jar with enhanced operation capabilities while reducing or avoiding the possibility of accidental unauthorized actuation of the jar mechanism.